1. Field of Invention
The present invention relates to a vascular implant that is implanted into an artery for repair or bypass of arterial injury. The vascular implant includes a stent-graft that is delivered intraluminally into an artery for repair of a vascular lesion and more specifically for repair of abdominal aortic aneurysm. The vascular implant further includes an attachment means that provides attachment of a stent-graft to a vessel wall.
2. Description of Prior Art
An abdominal aortic aneurysm is an outpouching of the wall of the aorta that can continue to expand over time possibly leading to rupture and mortality. The outpouched wall is generally filled with thrombus except for a generally tortuous pathway for blood flow through an opening in the thrombus. This thrombus can become organized over time as fibroblasts and other cell types infiltrate and form a more organized matrix material containing collagen and other tissue. Typically such aneurysms occur below or caudal to the renal arteries or veins and can extend distally into the right or left common iliac arteries or further distally into the right or left femoral arteries. The right renal vein which crosses over the ventral surface of the aorta can provide some support to the ventral surface of the aorta an help resist aortic distention. Aortic distention can occur very abruptly just distal to the renal vessels reaching a diameter of six centimeters or greater and causing the onset of accompanying symptoms and requiring repair. Generally the blood flow pathway through the thrombus does not follow these abrupt changes found in the vessel wall but rather continues on in a more direct albeit tortuous path through the thrombus found in the aneurysmal aorta. The abdominal aortic aneurysm can sometimes have a proximal neck or region where the aortic diameter appears to be of normal diameter. This proximal neck region is sometimes found just caudal to the renal vessels. The abdominal aortic aneurysm can sometimes also have a distal neck region located just proximal to the aorto-iliac bifurcation. In this minority of patients the abdominal aortic aneurysm does not extend to the iliac arteries or farther distally. Aortic distention in the majority of patients can extend into one or both of the iliac or femoral arteries; repair of this abdominal aortic aneurysm can involve treatment of the iliac and femoral arteries as well. The common iliac artery divides to form the external and internal iliac arteries. The internal iliac artery (also called the hypogastric artery) is important in providing a supply or blood to the pelvic region, genital organs, and other areas and is most often not aneurysmal. The external iliac artery is commonly involved in the aneurysm and extends distally along an oftentimes very tortuous path to form the common femoral artery.
Surgical repair of an abdominal aortic aneurysm is an extensive procedure associated with a high incidence of morbidity and mortality and requiring many days of hospital stay. Older patients are often not capable of withstanding the trauma associated with this surgery. Repair of abdominal aortic aneurysm intraluminally through access from the common femoral artery can provide the patient with an alternate method of treatment for abdominal aortic aneurysm without the accompanying surgical trauma and long hospital stay. Placement of an intraluminal stent-graft can be performed by an interventionalist using a minimal surgical cutdown to an ipsilateral common femoral artery for access of the device to the arterial system of the body. Generally an additional access site is placed percutaneously in the contralateral common femoral artery. It is often preferred to place at least one more access site cranial to the abdominal aortic aneurysm generally through an axillary artery or other artery of the arm. Spiral computed tomography, duel-plane angiography, intravascular ultrasound, magnetic resonance imaging, and fluoroscopy provide some of the diagnostic techniques used to determine the position, diameter, and length of the aneurysm such that an appropriate intraluminal prosthesis can be selected for intraluminal implantation. Placement of the intraluminal stent-graft requires that a leak tight seal be made between the stent-graft and the aorta and between the stent-graft and each of the iliac or femoral arteries if they are involved in the aneurysm. Failure to provide such a leak tight seal will allow blood flow at arterial pressure to access the space between the stent-graft and the outpouched aorta. Continued exposure to arterial blood pressure can result in farther expansion of the aneurysmal sac and could lead to sac rupture. Several intraluminal stent-grafts have been described for use in treatment of abdominal aortic aneurysms.
Barone describes in U.S. Pat. No. 5,578,072 an apparatus for repairing an abdominal aortic aneurysm. He describes a one-piece bifurcated aortic graft having a balloon expandable stent at one end to secure main trunk of the stent-graft to the aorta caudal to the renal arteries. The one-piece aortic graft has additional expandable stents positioned at the end of each leg of the bifurcated graft to secure the stent-graft to the iliac arteries. This design requires that the length of the main trunk and length of each limb be established prior to implantation using the diagnostic techniques described earlier. Due to the tortuous nature of the blood flow pathway, it is impossible to properly size the length of the graft using these diagnostic techniques prior to implatation. If the stent-graft is sized too short, then a portion of the aneurysm may be left unprotected. If the stent-graft is sized too long for example, then the blood flow to one or both of the internal iliac arteries may be compromised. The method of securing the main trunk of the stent-graft to the aorta caudal to the renal arteries described by Barone is also inadequate in many situations. A balloon expandable stent placed caudal to the renal vessels will very often be located within thrombus and will not have the strength or stability of the aortic vessel wall to support the stent or the stent-graft from migration caudally. Barone teaches that a securing means that is expanded outwardly over an axial length will hold the cranial end of the main trunk in position near the renal vessels. Barone also does not describe any means to prevent the stent-graft from being kinked or crushed as it travels through the thrombus laden blood flow pathway within the aortic aneurysm. Forces imposed upon the stent-graft due to the surrounding thrombus or thrombus organization could easily cause the stent-graft of Barone to become kinked or stenotic thereby impairing its performance. Barone discusses the need to place a stent proximal to the renal arteries for the case that the abdominal aortic aneurysm extends through the aortic region containing the renal arteries. He does not provide a suitable stent-graft for treating infrarenal aortic aneurysm with abrupt wall distension just distal to the renal vessels.
Parodi describes in U.S. Pat. No. 5,591,229 stent-graft devices that are similar to those described by Barone in the above patent. Additionally, Parodi describes a stent-graft for treatment of an abdominal aortic aneurysm that does not extend into the iliac region. This straight tubular stent-graft has a balloon expandable stent positioned at its cranial end for placement into the proximal neck of the aorta distal to the renal vessels. A balloon expandable malleable wire is placed at the distal end of the stent-graft to provide contact of the stent-graft with the aortic wall in the distal neck of the aorta. This stent-graft has a similar problem associated with estimating the graft length due to the tortuosity associated with the blood flow pathway through the thrombus laden aortic aneurysm. The other problem sited with the device described by Barone are similarly shared by the Parodi device.
Chuter describes in U.S. Pat. No. 5,693,084 a one-piece bifurcated stent-graft for treatment of abdominal aortic aneurysm having self expanding springs positioned at the proximal end of the main body and at the distal ends of each limb of the graft. The springs expand radially upon release to conform the ends of the stent-graft to the lumen of the aorta. This stent-graft suffers the same problem described for Barone in determining the length of the stent-graft prior to implant. Further, the stent-graft material is not supported throughout the entire stent-graft length thereby providing ample opportunity for stent-graft kinking and deformation within the aneurysm. Chuter has positioned six barbs that extend outward from the self expanding spring on the proximal end of the stent-graft. Due to the geometry of the springs, the positioning of the barbs into aortic wall rather than into the thrombus contained within the aneurysmal wall is not very precise. This can lead to stent-graft migration after a period of time post implant. Other problems associated with the Barone device similarly apply to the Chuter device.
McDonald describes in U.S. Pat. No. 5,676,697 a two-piece component bifurcated intraluminal stent-graft for treatment of abdominal aortic aneurysm. The first stent-graft component is a flexible tubular member with a side cut near the middle of the tubular member that opens up via a self expanding stent to form a waist region that is seated in the aorto-iliac bifurcation region. Two legs of the first stent-graft component are seated into each iliac artery using stents attached to the distal end of each leg. A second stent-graft component is introduced through one leg of the first component and allowed to self expand in the main trunk of the aorta and form a seal with the waist of the first component. The proximal end of the second component extends proximally within the aorta and makes a seal as it expands outwardly against the flow lumen. This device would have difficulty with positioning the proximal end of the second component within the proximal neck of the aorta. Extreme tortuosity found in the flow lumen of the aortic aneurysm would not allow this device to conform to its shape and would not allow a tight seal to be formed between the proximal end of the second component and the aorta. Difficulty in determining the appropriate length for each of the two components would limit the usefulness of this device.
Glastra describes in U.S. Pat. No. 5,632,763 a bifurcated component stent-graft assembly for treatment of abdominal aortic aneurysm. The assembly consists of a base stent-graft that is introduced into the main trunk of the aorta from an intraluminal approach. The base stent-graft has a generally cylindrical shape with a conical region located at the distal end. Two secondary cylindrical stents are introduced through two branching arteries, one in each leg and are seated in the conical region of the base stent-graft. This assembly has several potential problems associated with it. Determining the appropriate length of the base stent-graft and each of the secondary stent-grafts cannot be accurately performed considering that all of the arteries involved can be very tortuous and difficult to estimate in length. The seal that is required at the junction of the main to the secondary stent-grafts may have a tendency for leakage due to the geometry of that junction. Glastra describes two cylindrically shaped secondary stent-grafts that are placed adjacent to each other and are required to expand out and seal against a larger cylindrical base stent-graft; this seal would be difficult to form and maintain. Glastra does not address specific means for attachment of the proximal end of the base stent-graft to the aorta.
Marcade describes in U.S. Pat. No. 5,683,449 a modular system for forming a bifurcated stent-graft for use in treating abdominal aortic aneurysm. The system includes a number of components that are delivered intraluminally to the site of the aneurysm and brought into contact with each other within the aneurysmal space. The primary graft member has a proximal stent at one end and has an decreasing diameter as the stent-graft extends towards its distal end. The base member has a Y-shaped structure with a proximal end that contacts the distal end of the primary graft member. The base member also forms two branches on its distal end, each branch being brought into contact with a tubular graft member that extends into an iliac artery. This modular system still requires that each individual component be sized for length and diameter in order to fit the vast differences found between abdominal aortic aneurysm patients. Each junction between individual components is also a site for potential leakage of blood into the space between the stent-graft and the native arterial conduit. Marcade shows approximately five barbs positioned on the proximal stent. Due to the geometry of the stent it is not possible to obtain precise positioning of the barbs into the aortic wall tissue to ensure long term anchoring that would prevent stent-graft migration and maintain an adequate leak tight seal.
Vorwerk describes in U.S. Pat. No. 5,562,724 describes a component bifurcated device for treating abdominal aortic aneurysm consisting of a main body and two tubular stent-grafts. The main body has an open proximal end and a distal bag-shaped end with two outlet openings formed in it. Two tubular stent-graft legs can be introduced through the iliac arteries of the patient and attached to the two outlet openings of the main body. Sizing the appropriate length of the main body in addition to the two stent-graft legs is difficult due to the tortuosity found in the blood flow pathway of the aorta and iliac arteries. Leakage at the attachment site of the stent-graft legs to the main body also is a major concern.
Palmaz describes in U.S. Pat. No. 5,683,453 and Marin in U.S. Pat. No. 5,507,769 two tubular stent-grafts that travel in parallel from the infrarenal aortic neck to each iliac artery. Each stent-graft has a stent positioned at each end of the tube to form a seal with the native artery. This system would also have difficulty in determining the appropriate length of the stent-graft due to vessel tortuosity. In addition, this system requires that the two proximal stents deform against each other and with the proximal neck of the aorta to form a leak tight seal; it is not likely that an appropriate seal or attachment to the proximal aortic neck would be made. Extending a plurality of stent tubular members farther within the length of stent-graft create a stent-graft that is too stiff to pass through a tortuous iliac artery to reach the site of the abdominal aortic aneurysm.
Egoda describes in U.S. Pat. No. 5,591,228 a method of introducing a bifurcated stent-graft for abdominal aortic aneurysm treatment using three access points into the arterial vasculature. As with other intraluminal stent-graft procedures, two access sites involve the common femoral arteries. Egoda describes a third access site made in the left subclavian artery through which the stent-graft can be introduced. This method may allow better control over both ends of the stent-graft during implantation. The length of the stent-graft must still be determined prior to implant and estimation of the length of the blood flow pathway is difficult to determine using standard diagnostic equipment due to the tortuosity of the vessels involved in the aneurysmal dilation.
A one-piece endovascular graft is described by Piplani in U.S. Pat. No. 5,824,039 for treating a bifurcated abdominal aortic aneurysm lesion. This device has springs located at inlet and outlet ends to hold the graft in place. The springs also have barbs attached. The springs have a large zig zag appearance similar to other prior art attachment means and the barbs are not well protected from inappropriate snagging prior to deployment of the endovascular graft.
Modular intraluminal prosthesis are described by Lauterjung in U.S. Pat. No. 5,824,036 and by Fogarty in U.S. Pat. No. 5,824,037. Lauterjung describes a composite system using a magnetic tipped guidewire to assist in the assembly of the prosthesis and employs a stent at the ends of the prosthesis and elsewhere. Fogarty describes a self-expanding or resilient frame with a plastically deformable liner over the frame limiting the resilient expansion. Each of these two composite or modular systems shares similar problems to the composite systems described earlier, including the potential for leakage at the junction sites as well as leakage at the junction of the prosthesis with the vessel lumen.